KTLS cells in e13.5 fetal liver from +/+, +/-, and -/- PU.1 embryos. (A) Cells obtained from representative e13.5 fetal livers were incubated with a blocking antibody to Fc receptor (2.4G2) and then were stained with Sca-1^TexasRed, c-Kit^APC, Lin^PE, and Thy-1.1^FITC. Cells expressing Sca-1 and c-Kit (left) were analyzed for Thy-1.1 and lineage marker expression (right). (B) The absolute number of KTLS and (C) KLS cells in PU.1^+/+ and PU.1^-/- fetal livers is indicated (for -/- embryos, n = 2, e12.5; n = 6, e13.5; n = 8, e14.5; and n = 6, e15.5; for +/+ embryos, n = 2, e12.5; n = 2, e13.5; n = 6, e14.5; and n = 5, e15.5). Error bars indicate ± SEM.